Reduction of Levels of Volatile Components Associated with the "Beany" Flavor in Soymilk by Lactobacilli and Streptococci

ABSTRACT: Methanol, acetaldehyde, ethanol, and hexanal were the 4 major volatiles detected in unfermented soymilk. Eight of the cultures of lactobacilli or streptococci completely eliminated hexanal in the soymilk during fermentation. However, there were considerable variations in the effects of the cultures on the other 3 compounds. All 8 caused significant reduction in levels of methanol. Streptococcus thermophilus OSU-2 was the only culture that significantly lowered the concentration of ethanol in the soymilk. All except Lactobacillus acidophilus C19 and Lactobacillus casei E5 significantly lowered the level of acetaldehyde. Of the cultures tested, L. acidophilus L1 offered the best potential for producing fermented soymilk with an improved volatile profile.     

Formulation and Processing of a Heat Stable Calcium-fortified Soy Milk

Calcium-fortified soy milk (200 mg/100g) was formulated by adding water (85–90°C) full-fat soy flour (10%), sucrose (2.75%) and soy protein isolate (2.25%). Following homogenization, the blend was twice clarified and pasteurized at 65°C/30 min before refrigeration. Samples of the soy milk (45°C) were adjusted to pH 8 before adding calcium lactogluconate (1.55%) and varying amounts of sodium hexametaphosphate or potassium citrate. Samples with 1.25% potassium citrate the best heat stability. For successful calcium fortification, it is recommended to maintain a calcium-to-protein ratio < 38 mg/g and to use an appropriate sequestering agent at a molar ratio of 0.8/mole calcium.     

In vitro and in vivo Studies on the Antioxidant Effects of Soymilk Fermented with Streptococcus thermophilus grx02

Soymilk fermented with Streptococcus thermophilus grx02 (FSM) was evaluated for its antioxidant properties. Antioxidant effects of FSM in vitro were measured with 2, 2-diphenyl-1-picrylhydrazyl (DPPH) based assay and by determining the inhibitory effect on the formation for malonyldialdehyde (MDA), and on the ability to chelate ferrous ions; the respective average IC₅₀ values were 49.5, 24.2 and 8.7 mg/mL. Antioxidant enzymatic activities in liver of alcohol-fed mice, biochemical markers in serum and an index of lipid peroxidation were determined, and additionally the changes in hepatocytes of ICR mice were compared. The results showed that, compared with the control group, alanine transaminase (ALT) activity, aspartate transaminase (AST) activity and triglycerides (TG) of negative group increased (p < 0.05). Moreover, the serum ALT and AST activities of FSM group was lower than negative group (p < 0.05). However, there was no significant difference (p > 0.05) in the albumin (ALB) and total protein (TP) values (in positive, negative, control, and FSM groups) in the serum. Compared with the negative group, alcohol dehydrogenase (ADH), superoxide dismutase (SOD) activities and glutathione (GSH) content increased in liver (p < 0.05) in FSM group. The MDA of FSM group in liver was lower than the negative group (p < 0.05).     

生物解离对豆乳体系稳定性的研究

本文研究了碱性蛋白酶生物解离0、10、20和30 min条件下豆乳体系的粒径分布、Zeta电位、流变学特性、乳化活性及乳化稳定性的变化。并通过多重光散射稳定性分析考察豆乳体系的稳定性。研究结果表明,当生物解离20 min时,豆乳体系的平均粒径为456 nm,豆乳的粒径主要分布在100~1000 nm,随着生物解离时间的增加,粒径分布更集中,平均粒径不断降低。当生物解离作用时间为30 min时,电位绝对值最大为30.3 mV。但随着解离时间的增加,乳化活性及乳化稳定性在一定程度上降低。另外,生物解离不会改变豆乳的流体性质。多重光散射分析表明,豆浆体系的粒径更加均匀和稳定。综上,生物解离技术可作为提高豆乳体系稳定性的一种手段。     

Germination improves the functional properties of soybean and enhances soymilk quality

The effects of soybean variety and germination time on structural changes, antinutritional factor content, antioxidant activity of germinated soybean, and on the functional properties of soymilk were comprehensively investigated. The results showed that the antioxidant activity increased with increasing germination time. The content of antinutritional factors decreased with increasing germination time. Soybean varieties with the lowest tannin and trypsin inhibitor content were DN690 and HJ1. Lipoxygenase activity and phytic acid content showed no significant differences among soybean varieties. The content of α-helices and β-turns in soybean protein decreased with increasing germination time, while the content of β-sheets was increased. Soybean protein was progressively broken down into smaller molecular peptides during the germination process. The digestion and content of soluble protein in soymilk increased with germination. In summary, we show that germination is an effective, cheap, and green method that improves the functional properties of soybean and soymilk.     

Isoflavone Profiles and Kinetic Changes during Ultra‐High Temperature Processing of Soymilk

Isoflavone profile is greatly affected by heating process. However, kinetic analyses of isoflavone conversion and degradation using a continuous industry processing method have never been characterized. In this study, Proto soybean was soaked and blanched at 80 °C for 2 min and then processed into soymilk, which underwent UHT (ultra‐high temperature) at 135 to 150 °C for 10 to 50 s with a pilot plant‐scale Microthermics processor. The isoflavone profile was determined at different time/temperature combinations. The results showed that all isoflavone forms exhibited distinct changing patterns over time. In the soymilk under UHT conditions, the degradation (disappearance) of malonyldaizin and malonylgenistin exhibited first‐order kinetics with activation energies of 59 and 84 kj/mole, respectively. At all UHT temperatures, malonylgenistin showed higher rate constants than malonyldaidzin. However, malonylglycitin changed irregularly under these UHT temperatures. The increase of genistin, daidzin, glycitein and acetlydaidzin during heating demonstrated zero‐order kinetics and the rate constants increased with temperature except for the conditions of 145 to 150 °C for 50 s. Overall, genistein series exhibited higher stability than daidzein series. Under all UHT conditions, total isoflavone decreased from 12% to 24%.     

Insolubilisation and gelation of heat–frozen soymilk

Soymilk prepared from soybean seed was heated and frozen. After thawing, precipitation was shown to occur in soymilk. Precipitation from heated and frozen soymilk increased with increase in heating time. Precooling treatment (−5°C) before freeze‐storage of heated soymilk resulted in gel‐like solidification of soymilk. The gel strength of the freeze‐gel formed from soymilk was related to the heating time and the viscosity of the soymilk before freezing. © 1999 Society of Chemical Industry     

纯大豆发酵豆乳的风味物质与微观结构的初探

在研究纯大豆发酵豆乳的基础上,对产品的风味物质与微观结构进行了初步分析和探索。经过色、质谱联用仪分析检索出纯大豆发酵豆乳中风味物质相对百分含量在0.5以上的主要成分与相对百分含量,并经过扫描与透射电子显微镜对产品发酵中产物与成品的微观结构分别进行了观察与分析。     

益生菌混合菌种在发酵豆乳中的优化

采用益生菌混合物AST和TLB分别在42℃进行豆乳的发酵,在发酵豆乳的发酵和贮存过程中(4℃下28d),观察pH值和活菌数的变化情况。在AST益生菌混合物(嗜酸性乳杆菌,双歧杆菌和嗜热链球菌)的培育下,42℃下发酵时间减少到8h。但嗜酸性乳杆菌在冷藏的过程中生存状态较差,其活菌数在冷藏后一周后未达到标准。将豆乳在42℃下用TLB益生菌(嗜热链球菌,保加利亚乳杆菌和动物双歧杆菌乳酸亚种Bb12)进行发酵,结果发酵时间缩短到4h,双歧杆菌活菌数目的对数增加了约一半,而且经过28d的冷藏,细菌数仍然维持在107 CFU/mL以上。